This invention relates to apparatus for inspection of gems, and more specifically to apparatus for distinguishing a true diamond from simulated diamonds including moissanite.
The jewelry industry is often confronted with simulated diamonds of little value that are being offered as true diamonds of great value. Methods to differentiate the two have used measurement of thermal conductivity as disclosed in U.S. Pat. No. 4,255,962 issued Mar. 17, 1981 to Ashman; U.S. Pat. No. 4,616,939 issued Oct. 14, 1986 to Gitlis; and U.S. Pat. No. 4,488,821 issued Dec. 18, 1984 to Wenckus. These are based on the fact that most simulated diamonds have a much lower thermal conductivity than true diamond. There is a simulated diamond currently marketed that has a thermal conductivity so close to true diamond that it cannot be detected by these devices. This material is moissanite, a form of silicon carbide with physical properties very close to true diamond. As discussed in U.S. Pat. No. 6,043,742 issued Mar. 28, 2000 to Austin, moissanite has been distinguished in the past by measurement of electrical conductivity. Moissanite conducts electricity much more than true diamond, which is an excellent electrical insulator. Austin teaches a device that applies an alternating current to the stone, and indicates by an audible signal if the conductivity is so great as to eliminate diamond. Absence of a signal indicates that the item is a true diamond. However, if the item is a good insulator but not a diamond, his device will not sound, thereby falsely indicating that it is a true diamond. This may occur with a glass specimen, from an insulating coating, poor contact to the item, or other conditions.
It is accordingly an object of the invention to provide an apparatus and method that will differentiate between true diamond and moissanite as well as other simulated diamonds. It is another object that this be achieved with a single, hand-held instrument that is easy to operate without special skills. The apparatus of the invention is a hand-held device having a probe with a small contact at one end for contacting the surface of the gem to be tested. While the probe is contacting the gem, a first measurement is made of thermal conductivity, emitting an audible signal if the item has the high thermal conductivity of diamond, followed by a measurement of electrical conductivity. If the tests reveal that the item has the high thermal conductivity and the very low electrical conductivity of true diamond, the audible signal continues, indicating that the item is a true diamond, if, however, a high electrical conductivity is detected, a different audible signal is then emitted to indicate that it is moissanite. In addition, a red LED is lit if it is moissanite, and a green LED is lit if it is a true diamond. There is no danger in falsely indicating a true diamond because of poor contact of the probe. Indeed, the operator may try repositioning the probe if no signal is given.
These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.